1. Field of the Invention
The present invention relates generally to the field of loudspeakers and in more particular to an improved outer-suspension design for a loudspeaker.
2. Description of the Prior Art
In the design of loudspeakers, the suspension system in any loudspeaker is normally comprised of two elements, the surround (front or outer suspension) and the spider (rear suspension). The surround is the mechanical device which holds the outer edge of the diaphragm/cone of the loudspeaker. Often the word "roll" is used in place of "surround" when describing the front suspension. Surrounds can be constructed from several materials including rubber, compressed foam rubber, corrugated cloth, paper, plastic, etc. Roll surrounds have a single, large, semi-circular corrugation typically constructed from rubber, compressed foam rubber or treated fabric.
Surrounds help keep the cone centered and provide a portion of the restoring force that keeps the voice coil in the gap created between the pole piece and top plate of the loudspeaker. The surround also provides a damped termination for the edge of the cone. The choice of thickness and material type for surround construction can greatly alter the response of the loudspeaker.
The spider, commonly constructed from treated corrugated fabric, also keeps the voice coil concentric to the pole piece, as well as providing a portion of the restoring force that maintains the voice coil within the gap. The stiffness of the spider can greatly affect the loudspeaker's resonance. The spider also provides a barrier for keeping foreign particles away from the gap area.
Surrounds are one of the primary limiting factors in designing long-excursion loudspeakers. Excursion is defined as the amount of linear length the cone body can travel. With the conventional small roll diameters currently in use, the excursion is often limited by the surround's physical limits. Larger surrounds cannot be used without an attendant loss in effective cone area for a loudspeaker of given outside diameter, thus, creating an inevitable trade-off. Excursion and cone area are the two factors which contribute to a loudspeaker's volume displacement. The higher the volume displacement capability of a loudspeaker, the greater the loudspeaker's ultimate low frequency output potential can be.
In addition to controlling the linear motion of the cone, the surround also acts as a major centering force for the loudspeaker's voice coil. This centering force prevents the voice coil and former from rocking and rubbing against the pole piece or top plate.
Presently, the surround is typically glued to the inner top edge of a flat extension or rim on the outside of the loudspeaker's frame, which also acts as the loudspeaker's mounting flange. With such assembly method, a significant amount of cone area is sacrificed, relative to the loudspeaker's overall footprint (outside diameter). The cone area is a major contributing factor to a loudspeaker's output and efficiency. The sacrifice in cone area is seen as a necessary evil because of the need to provide an accessible mounting flange for the loudspeaker.
Furthermore, current methods for replacing moving parts of a cone loudspeaker, for the purpose of repair, require special skill, tools and adhesives. Typically, the moving parts are cut away and the loudspeaker frame and motor structure (magnet and metal parts that complete the magnetic circuit) are stripped down with chemicals or hand scraped to remove adhesive residue. Once the frame is stripped, new moving parts must be glued together, aligned carefully and glued to the loudspeaker frame. This repair or replacement assembly process normally is handled by trained loudspeaker technicians and requires specialized gauges or alignment spacers for each loudspeaker, as well as a high degree of precision in order to be successful.
Some current small dome loudspeakers, primarily tweeters, and compression drivers feature the ability to quickly remove and replace their moving parts. This is facilitated greatly in these designs due to the lack of a rear suspension or spider. In these designs, the diaphragm, voice coil and surround are typically attached to a rigid frame which bolts or screws to the top plate of the loudspeaker. The frame is usually located with holes which line up to pegs on the motor structure for alignment. In such designs, the loudspeaker must be removed from its mounting location to perform the repair.
One product currently on the market, provides a woofer in which the motor structure (i.e. magnet, back plate, pole piece and top plate) is removed from the frame so that the voice coil can be inspected. However, the moving parts (roll, cone body, dust cap, voice coil and spider) remain attached to the loudspeaker's frame. Another product on the market, provides a cone loudspeaker which features a screw-down spacer between its dual spiders or rear suspensions. The spacer screws through the frame to the top plate of the loudspeaker. The screws do not provide the necessary physical constraints to align the voice coil within the magnetic gap. This is still done with gauges (alignment spacers). The surround is glued to the frame in a conventional manner and the spider is glued to the spacer. Accordingly, this product fails to provide for easy field replacement of its parts.
Additionally, a loudspeaker must be carefully optimized for its intended task. Changes in its moving mass, motor strength, voice coil winding length/gauge/thickness or suspension compliance radically affect the performance of the loudspeaker. There are inevitable tradeoffs in the process of loudspeaker design. These tradeoffs must be carefully balanced with the intended task of the loudspeaker in mind, i.e. concert sound reinforcement, automotive sub-bass, home-theater, etc. With woofers, the intended enclosure type affects the design of the driver as well.
Ideally, an end user chooses a loudspeaker which will work best in his or her intended application. The most expensive components of a loudspeaker are its non-moving parts, which generally include the loudspeaker frame, and the motor structure. The moving parts of the loudspeaker generally represent a smaller portion of the total cost of the loudspeaker. If the user's operating conditions change, the loudspeaker may no longer be well-suited and is likely to be replaced with a more appropriate loudspeaker. Such is the case even if there is nothing wrong with the original loudspeaker and usually amounts to a relatively significant expenditure each time the operating conditions change.
Some existing small dome loudspeakers, primarily tweeters, and compression drivers feature the ability to remove and replace their moving parts, in the event of failure. Different impedance diaphragms are offered that will work in the same motor structure. The basic mission of the loudspeaker is not changed, only the load presented to the amplifier. However, the prior art fails to provide for reconfiguring the same motor structure in the field for different applications and enclosure types, specifically for low frequency woofers.
Additionally, the prior art fails to provide for a loudspeaker design which provides for relatively quick field replacement of the moving parts of a cone type loudspeaker, and in more particular to cone type loudspeakers which feature a rear suspension or spider in addition to the surround. The prior art also fails to provide a surround which is attached to the outer edge of the loudspeaker frame for improved overall displacement capability. Furthermore, the prior art fails to provide for a removable surround. It is therefore, to the effective resolution of the aforementioned problems and shortcomings of the prior art that the present invention is directed.